Histopathology study and expression of immune-related genes in intestine of black tiger shrimp Penaeus monodon

Abstract

In all previous studies, to induce an infection in shrimp, the bacteria were directly injected into the shrimp body and as a consequence the initial step of a natural interaction was omitted. In this study, an immersion technique was used, which is a more natural way of establishing an infection, to study infection in black tiger shrimp (Penaeus monodon). Vibrio harveyi strain 1526 is highly pathogenic to post-larvae shrimp (PL) but in contrast, juvenile shrimp can survive even at a higher dose of bacteria used to infect PL. In PL, V. harveyi causes a massive destruction of the digestive system, especially in the hepatopancreas and in the anterior midgut, while mild infection was observed in the hepatopancreas and only some part of the gut has lesions and signs of heavy infection. According to the histopathological results they show that both PL and juvenile have an efficient cellular defense mechanism including phagocytosis and the prophenoloxidase activating system to fight the infecting bacteria. In addition, the effects of infections were studied on immune gene expression in the intestine. Expression patterns of several genes (ALF2, ALF3, crustin, penaeidin, PrX, proPO, C-lectin, BGBP, MMR, TL5a1, TL5a2, ficolin, Lysozyme, MnSOD and mucin-like PM) were examined by reverse transcription-polymerase chain reaction (RT-PCR) and real-time PCR. Results indicated prominent alteration on expression of C-lectin whereas that of the antimicrobial peptides (AMPs; ALF3, crustin, and penaeidin), TL5a1 and mucin-like PM was also slightly changed. The V. harveyi-immersion did not affected expression of ALF2, PrX, proPO, BGBP, MMR, TL5a2, ficolin, Lysozyme and MnSOD. Besides, the TL5a1 transcript was highly expressed in the posterior part of the hindgut but the mucin-like PM transcript was highly expressed in the anterior and middle midgut.